Data Zone
Justification of Red List category
This species has a very large geographic range size (extent of occurrence >13 million km2 in both the breeding and non-breeding seasons), and so does not approach Criterion B thresholds. It also has a large estimated population size (900,000 to 1,200,000 mature individuals), and so does not approach Criteria C or D thresholds. Although the data presented in Smith et al. (2023) indicate rapid declines exceeding 40% over three generations (c. 19 years), other populations are evidently not declining as rapidly. In the East Atlantic Flyway (including Western Europe), van Roomen et al. (2022) recorded an increase in abundance between 1979 and 2020, while the trend of birds wintering in SW Asia, Eastern and Southern Africa appears relatively stable (Nagy and Langendoen 2020). These latter trends represent a majority of the species' global range. Moreover, the data in Smith et al. are presented with significant bounds of uncertainty, and eBird data (Fink et al. 2023) suggest, in contrast to Smith et al., a stable population trend. Collating all available data, the global population of this species is estimated to have declined by 0-19% over the past three generations. Although the population is declining, it does not currently appear to be declining at a rate approaching Criterion A thresholds. Hence, the species continues to warrant listing as Least Concern.
Population justification
Population size very large. Bart et al. (in prep.) estimated a total of c.700,000 breeding adults in Arctic Canada, which is thought to comprise the majority of the global population. An additional population of at least 200,000 breeding individuals is suspected by summing populations from elsewhere (based on data collated by Wetlands International [2023]). The global population is therefore suspected to number 900,000-1,200,000 to account for uncertainty over the population size of birds in Siberia. The population size of birds using the East Asian-Australasian Flyway was estimated at 30,000 (Hansen et al. 2022).
Trend justification
Global population trend suspected to be declining from migration/non-breeding count data, but this is being driven almost entirely from declines in the American flyway, with other populations stable or perhaps even increasing.
In the East Atlantic Flyway (including Western Europe), van Roomen et al. (2022) recorded an increase in abundance between 1979 and 2020, while the trend of birds wintering in south-west Asia, Eastern and Southern Africa appears relatively stable (Nagy and Langendoen 2020). The trend from South Asia is poorly known, but declines have been reported in reporting rates of citizen science data in India (SoIB 2023). In the East Asia-Australasia Flyway, the population trend is not well understood but is probably either stable or perhaps now declining slowly (see Lagendoen et al. 2021). Rapid declines have been reported only from non-breeding range in North America: Smith et al. (2023) estimated a population reduction equivalent to 47.8% over three generations, though with wide confidence intervals between a reduction of 68.8% and 10.5%. These data are also used in the Avian Conservation Assessment Database December 2023 update (Partners in Flight 2023). However, also in the Americas Fink et al. (2023) estimated a broadly stable trend (0% median trend, with +10% to -11% as confidence intervals) over three generations, thus rendering the trend in the Americas somewhat uncertain.
Collating all available data, the global population of this species is suspected to have declined by 0-19% over the past three generations. Future rates of decline are considered uncertain.
Breeds on high-arctic tundra including in Arctic Canada (which hosts majority of global population), northernmost Alaska (USA), Greenland, Norway and Siberian Russia. In winter can be found in suitable habitat almost anywhere in the world!
Behaviour This species is a full long-distance migrant that travels mainly via offshore and coastal routes using a number of favoured stopover sites (del Hoyo et al. 1996). It breeds from June to mid-July in solitary pairs (del Hoyo et al. 1996), departing the breeding grounds between mid-July and early-September (Hayman et al. 1986). The species usually occurs in small flocks on migration (Johnsgard 1981) although it may aggregate into larger flocks at stopover sites (Hayman et al. 1986), and in winter it forages in small to very large flocks (del Hoyo et al. 1996). Habitat Breeding The species breeds in the high Arctic on barren, stony tundra with well-drained ridges (Johnsgard 1981, del Hoyo et al. 1996), gentle slopes or level alluvial plains supporting scattered vegetation of willow Salix spp., Dryas spp. and saxifrage Saxifraga spp. usually less than 200 m above sea-level (Johnsgard 1981). Non-breeding On passage the species may occur on inland freshwater or saline lakes (del Hoyo et al. 1996) but it is largely coastal during the winter, inhabiting open sandy beaches exposed to the sea, the outer reaches of estuaries, rocky and muddy shores, mudflats (del Hoyo et al. 1996) and coral reefs (Urban et al. 1986). Diet Breeding When breeding the species takes insects (especially adult and larval Diptera, Coleoptera and Lepidoptera) as well as spiders and crustaceans (del Hoyo et al. 1996). On arrival on the breeding grounds the species may also complement its diet with plant matter (e.g. seeds, saxifrage buds, moss and algae) (del Hoyo et al. 1996) before invertebrate prey becomes available (Johnsgard 1981). Non-breeding During the winter its diet consists of small molluscs, crustaceans, polychaete worms and adult, larval and pupal insects (e.g. Diptera, Coleoptera, Lepidoptera, Hemiptera and Hymenoptera), as well as occasionally fish and carrion (del Hoyo et al. 1996). Breeding site The nest is a shallow depression on the bare earth (del Hoyo et al. 1996) of stony well-drained ridges, gentle slope or level alluvial plains (Johnsgard 1981).
Species is threatened by pollution, which alongside other anthropogenic threats at wintering and migratory stopover sites are thought to have been the cause of significant declines over the past 30 years. Oil pollution is particularly concerning due to frequent offshore petroleum activities, consistent small-scale spills, and potential long-term sublethal effects. These factors pose a serious threat to shorebird habitats (Labarrère, 2016). The extensive time that C. alba spends in marine environments heightens its susceptibility to oil spills, which disrupt both foraging and migration behaviours.
Climate change poses another significant threat. A 17-year study focusing on C. alba breeding in Greenland (Reneerkens et al. 2016) highlighted that a substantial portion of the population depends heavily on the Wadden Sea during migration (Loonstra et al. 2016; Reneerkens et al. 2020). Over this period, the emergence of crucial food sources such as insects and spiders has shifted earlier due to earlier snow melt. However, the birds have not adjusted their breeding timing accordingly, leading to a phenological mismatch. This mismatch results in a critical misalignment between the peak food demand of C. alba chicks and the availability of sufficient food resources. Predicted increases in temperature due to climate change may also eliminate almost all nesting habitat and alter topography at such a rate that invertebrate prey will be negatively impacted (Myers 1988).
Habitat degradation due to urban development and wetland loss further compounds these challenges, particularly in key staging areas like Delaware and Chesapeake Bays (Macwhirter et al. 2020).
Disturbance poses a threat as they inhabit shoreline habitats extensively used by humans for recreation. Activities such as beach recreation can disrupt the species ability to forage and rest. The intensity of human disturbance varies across different sites and times of the year but is widespread and chronic in heavily populated areas. Off-road vehicles, pedestrians, and especially unleashed dogs often disturb the species (Thomas et al. 2003). While individual incidents may seem minor, the cumulative impact of continuous human disturbances compromises the quality of the species feeding and resting sites (Payne 2010).
The species is also susceptible to avian influenza so may be threatened by future outbreaks of the virus (Melville and Shortridge 2006). In the Chinese, North Korean and South Korean regions of the Yellow Sea (East Asian flyway route) this species is threatened by the degradation and loss of wetland habitats through environmental pollution, reduced river flows and human disturbance (Kelin and Qiang 2006).
Conservation Actions Underway
The species is listed in Annex II of CMS. It is not listed on the annexes of the European Union (EU) Birds Directive, but is covered by the general protection regime provided by Article 1 of the Directive to all naturally occurring wild species in the EU. In 2021, the 'Regional Flyway Initiative' (RFI) was set up by the Asian Development Bank, with technical support from BirdLife International, with the aim of protecting and restoring priority wetland ecosystems and the associated ecosystem services they provide in the East-Asian Australasian Flyway (EAAF), the most threatened flyway globally. The Initiative is slated for implementation in 10 East, South and South-East Asian countries: Mongolia, China, Bangladesh, Viet Nam, Cambodia, Lao PDR, Philippines, Thailand, Malaysia and Indonesia, all of which are used by C. alba on northbound and southbound migrations between breeding and wintering areas, and many also for wintering. The RFI will mobilise large-scale financing to support the protection, sustainable management and restoration of at least 50 priority wetlands across ten Asian countries, with an initial financing commitment of $3 billion from the ADB (BirdLife International 2022). Over time, the RFI aims to enhance and expand the existing efforts in conserving and managing priority wetlands identified on the basis of supporting globally significant congregations of migratory waterbirds, and leverage on collaborative opportunities with stakeholders including national governments, civil society organizations, communities, regional organisations like the East Asian-Australasian Flyway Partnership. A large portion of this species' breeding population is covered by PRISM surveys in North America, enabling regular monitoring.
Conservation Actions Proposed
Ensure the continuation of regular monitoring. Research threats to understand why some populations in the Americas appear to be declining rapidly.
Text account compilers
Berryman, A., Malpas, L., Everest, J., Chad, E., Butchart, S., Ashpole, J, Ekstrom, J.
Recommended citation
BirdLife International (2024) Species factsheet: Sanderling Calidris alba. Downloaded from
https://datazone.birdlife.org/species/factsheet/sanderling-calidris-alba on 24/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 24/11/2024.